Expansile bone lesion in the sternum of an MM-engrafted mouse injected IC with ex-vivo human MM cells (× 20).

Upper panel: The box indicates the expansile bone lesion. B = bone, PC = human plasma cells. Lower panel: Higher power view of the expansile lesion (× 100), arrow = expansile lesion. Sequential sections were stained with antihuman kappa chain, or antihuman lambda. All the plasma cells, which were derived from a patient with IgK myeloma, were strongly positive for kappa. None stained with antilambda.